This invention relates to dielectric storage targets and, more particularly, to membrane type dielectric storage targets and methods for fabricating same. This is a continuation in part of U.S. patent application Ser. No. 806,534, filed Mar. 18, 1969.
Dielectric storage films have been used to coat apertured conductive target electrodes in electron beam storage tubes. Such electrodes may take the form of fine wire mesh grids. There are many wire mesh target electrode structures shown in the prior art. Frequently, these structures exhibit thick film dielectric layers contiguous to the wire mesh, the mesh apertures being plugged with conductive material. The metal plugs are inserted in order to offset the combined capacitance effects of the metal mesh and the thin dielectric film coatings. In this regard, reference may be made to Teal (U.S. Pat. No. 2,630,101) and H. R. Day (U.S. Pat Nos. 3,020,433 and 3,116,191). Such prior art structures, however, do not relieve the mechanical stress exerted by the film on the supporting mesh. Also, the use of metal plugs to correct thick film capacitance distortion increases rather than decreases the mechanical burden carried by the wire mesh.
It is, accordingly, an object of this invention to devise a dielectric storage target electrode in which mechanical stress on a supporting mesh is minimized. Relatedly, it is desired to reduce the leakage of charge as well as the capacitance formed by the dielectric membrane element to the surrounding conducting mesh.
In the prior art, the forming of conductive surfaces on either side of a dielectric has required the use only of those dielectrics through which metal will diffuse at elevated temperatures. Thus, a nickel mesh with a gold coating covered with a zinc sulphide dielectric layer permits the gold from the nickel to diffuse through the dielectric onto the other side. Unfortunately, dielectrics such as zinc sulphide are relatively poor and exhibit undesirably high leakage currents if the operating temperature exceeds room temperature. Dielectric membranes formed from higher quality dielectric materials do not readily permit diffusion of a metal therethrough.
It is, accordingly, another object of this invention to devise a membrane type dielectric storage target and method for making same in which the wire mesh support on one surface of the film is exactly imaged on another portion of the dielectric film and further that the dielectric be of high quality. Relatedly, it is desired that the method for fabrication should not be dependent upon the diffusion of metal through the dielectric portion of the target.